The present disclosure relates to a night vision goggles aided flight simulator system and method for simulating night flight operations.
Traditional Night vision goggles (NVGs) and sensors like CCD and/or short wave infrared (SWIR) e.g. up to 2200 nm offer the opportunity to extend flight operations to the night. However, besides the usual costs of training during real flight, night flights pose additional restrictions. For example, in mid-summer it may not turn completely dark everywhere, the risk of crashing the airplane is higher than usual, the number of night-time flying hours in urban areas is limited to minimize sleep disturbance, and keeping the airport open outside regular hours introduces substantial financial costs. Accordingly, there is a need for NVG capable simulators to do NVG mission rehearsal and to familiarize flight-personnel with the fundamental and oftentimes surprising NVG visual illusions. The goal of a so-called “Level D” NVG simulator is to minimize the differences to the real world such that a user, e.g. pilot, can complete most of his training in the simulator.
In the real world, NVGs enhance the visibility of otherwise dark objects, but the NVG image is both i) degraded compared to and ii) different from the corresponding day view image. In addition, NVGs typically cause visual illusions that do not occur during the day. Because visual illusions are by definition difficult to distinguish, they are a prime cause for spatial disorientation and therefore of particular importance in NVG training. For example, NVG images usually represent luminous objects with bright circles around them, called halos. The size of these halos is typically independent of the distance to the bright object, and can therefore not be used as a distance cue. In addition, halos wash out all details in the direct surrounding of the bright object. Another example of an artefact is the so-called ‘chlorofyll effect’: grass and tree leaves appear particularly bright in an NVG image due to the high reflectance of chlorofyll in the near-infrared (NIR) region where the NVG has its highest sensitivity. While NVG simulated imagery may be generated in software using a dedicated head mounted display (HMD), it is desirable that a user can experience the simulation with the actual functioning NVGs to increase realism. However, simulating artefacts such as halos and realistic shadows with a simulation approach using actual NVGs in the simulator (so-called “NVG stimulation”), is difficult because it requires reproduction of extremely high contrasts encountered at night (e.g. cultural lights versus the rest of the world).
For example, U.S. Pat. No. 5,380,204 describes a currently used technique and system for night vision goggle aided flight simulation that allows a flight simulator operator wearing night vision goggles to view an approximate simulation of night vision goggle aided flight. A processor generates at least one look-up table of brightness values utilizing database sources including any selected options. A scene generation computer will then generate the scene image with the contrast based on values provided by the look-up table. An image display system displays the scene at light levels with sufficient dynamic range so that approximate simulation of night vision goggle aided flight is achieved. A neutral density filter can be placed over a CRT display if the CRT display as the display system cannot produce sufficient dynamic range.
For example, U.S. Pat. No. 6,196,845 B1 describes a visual display system and method for stimulation of night vision goggles using CRT displays. The display system includes a high resolution head tracked area of interest display for a rear projection video display. The system time multiplexes the display of raster and calligraphic images in the area of interest. The system also includes a method of calligraphic light point projection that conserves power by using a head tracked slow speed high sensitivity electromagnetic deflection system to position an electron beam which is modulated in X-Y position in a calligraphic fashion by a high speed secondary yoke to create intense light point images for the area of interest display.
However, the known methods are found to provide insufficient realism when used with dome based projection systems because the effective contrast generated is too low. There is yet a need for a (dome) projection based NVG aided flight simulation which includes the high dynamic range artefacts which occur in actual NVGs, such as bright light sources and dark shading.